Flexible display and method of manufacturing the same

ABSTRACT

A substrate for a flexible display is disclosed. The substrate has a film stress range that does not affect an electronic device such as a thin film transistor, and includes a barrier layer having excellent oxygen and moisture blocking characteristics, and a method of manufacturing the substrate. The substrate includes; a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and a barrier layer disposed on the plastic substrate, having a inti layer structure, wherein at least one silicon oxide layer and at least one silicon nitride layer are alternately stacked on each other, and having a film stress from about −200 MPa to about 200 MPa due to the at least one silicon oxide layer and the at least one silicon nitride layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/975,054, filed on Aug. 23, 2013 in the U.S. Patent and TrademarkOffice, which is a continuation of U.S. patent application Ser. No.13/087,300, filed on Apr. 14, 2011 in the U.S. Patent and TrademarkOffice, which claims priority from Korean Patent Application No.10-2010-0074979, filed on Aug. 3, 2010 in the Korean IntellectualProperty Office, the contents of all of which are incorporated herein byreference in their entireties.

BACKGROUND 1. Field

The present disclosure relates to a substrate for a flexible display,and a method of manufacturing the substrate.

2. Description of the Related Technology

Markets of liquid crystal display devices and organic light emittingdisplay devices are currently expanding to displays of digital cameras,video cameras, and mobile devices, such as personal digital assistants(PDAs) and mobile phones. The displays of mobile devices need to bethin, light, and moreover, unbreakable. In order to form a thin andlight display, a method of preparing a display by using a conventionalglass substrate, and then thinning the glass substrate mechanically orchemically has been introduced, besides a method of preparing a displayby using a thin glass substrate. However such methods are complicatedand the glass substrate may easily break, and thus the methods aredifficult to be actually used. Also, for the mobile devices to be easilycarried and to be applied to display devices of various shapes, thedisplays may be flexible to realize a curved surface. However, it isdifficult for the conventional glass substrate to have flexibility.

Accordingly, there have been attempts to manufacture a display device byusing a plastic substrate, but the plastic substrate has high level ofmoisture and oxygen penetration and is not suitable for a hightemperature process.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One aspect of the present invention provides a substrate for a thin,flexible display, which has film stress range that does not affect anelectronic device, such as a thin film transistor, and includes abarrier layer having excellent oxygen and moisture blockingcharacteristics, and a method of manufacturing the substrate.

According to the aspect of the present invention, the substrateincluding: a plastic substrate having a glass transition temperaturefrom about 350° C. to about 500° C.; and a barrier layer disposed on theplastic substrate, having a multi-layer structure, wherein at least onesilicon oxide layer and at least one silicon nitride layer arealternately stacked on each other, and having a film stress from about−200 MPa to about 200 MPa due to the at least one silicon oxide layerand the at least one silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a siliconnitride layer stacked on the first silicon oxide layer; and a secondsilicon oxide layer stacked on the silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a firstsilicon nitride layer stacked on the first silicon oxide layer; a secondsilicon oxide layer stacked on the first silicon nitride layer; a secondsilicon nitride layer stacked on the second silicon oxide layer; and athird silicon oxide layer stacked on the second silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a firstsilicon nitride layer stacked on die first silicon oxide layer; a secondsilicon oxide layer stacked on the first silicon nitride layer; a secondsilicon nitride layer stacked on the second silicon oxide layer, a thirdsilicon oxide layer stacked in the second silicon nitride layer; a thirdsilicon nitride layer stacked corn the third silicon oxide layer; and afourth silicon oxide layer stacked on the third silicon nitride layer.

The at least one silicon oxide layer included in the barrier layer mayhave compressive film stress. The at least one silicon nitride layerincluded in the barrier layer nay have tensile film stress.

The at least one silicon nitride layer may have a film density fromabout 2.5 g/cm³ to about 2.7 g/cm³.

The at least one silicon nitride layer may have a hydrogen atom contentfrom about 13% to about 17%.

Each of the at least one silicon nitride layer may have a thickness fromabout 200 Å to about 1000 Å.

Each of the at least one silicon oxide layer may have a thickness fromabout 1000 Å to about 3000 Å.

The plastic substrate may include at least one of polyimide,polycarbonate, polyphenylene sulfide, and poly(arylen ether sulfone.

According to another aspect of the present invention, there is provideda method of manufacturing a substrate for a flexible substrate, themethod including: providing a plastic substrate having a glasstransition temperature from about 350° C. to about 500° C.; and forminga harrier layer having a film stress from about −200 MPa to about 200MPa by alternately stacking at least one silicon oxide layer and atleast one silicon nitride layer on the plastic substrate.

The forming of the barrier layer may include high temperature depositionat a temperature from about 350° C. to about 400° C.

The barrier layer may include: a first silicon oxide layer; a siliconnitride layer stacked on the first silicon oxide layer; and a secondsilicon oxide layer stacked on the silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a firstsilicon nitride layer stacked on the first silicon oxide layer; a secondsilicon oxide layer stacked on the first silicon nitride layer; a secondsilicon nitride layer stacked on the second silicon oxide layer; and athird silicon oxide layer stacked on the second silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a firstsilicon nitride layer stacked on the first silicon oxide layer; a secondsilicon oxide layer stacked on the first silicon nitride layer; a secondsilicon nitride layer stacked on the second silicon oxide layer; a thirdsilicon oxide layer stacked on the second silicon nitride layer; a thirdsilicon nitride layer stacked on the third silicon oxide layer; and afourth silicon oxide layer stacked on the third silicon nitride layer.

The at least one silicon oxide layer included in the barrier layer mayhave compressive film stress. The at least one silicon nitride layerincluded in the barrier layer may have tensile film stress.

The at least one silicon nitride layer may have a film density fromabout 2.5 g/cm³ to about 2.7 g/cm³.

The at least one silicon nitride layer may have a hydrogen atom contentfrom about 13% to about 17%.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a substrate for a flexible display,according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a substrate for a flexible display,according to another embodiment of the present invention;

FIG. 3 is a cross-sectional view of a substrate for a flexible display,according o another embodiment of the present invention;

FIGS. 4 through 6 are diagrams for describing a method of manufacturing,a display device by using the substrate of FIG. 1, according to anembodiment of the present invention.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

While the invention have numerous embodiments, only some of suchembodiments will be illustrated in the drawings and described in detailin the written description. The present invention is not limited to theparticular embodiments, and there are changes, modifications andsubstitutes that do not depart from the spirit and technical scope ofthe present invention.

While terms of “first,” “second,” “third,” etc., are used to describevarious components., such terms do not carry the meaning of order. Theseterms are used only to distinguish one component from another. Also, inthe present specification, the terms of “including” and “having,” areintended to mean “comprising” so as to indicate the possibility ofexistence of any additional features, numbers, steps, actions,components, parts, or combinations.

Now, various features of the present invention will be described morefully with reference to the accompanying drawings, in which exemplaryembodiments of the invention are shown.

FIG. 1 is a cross-sectional view of a substrate 1000 for a flexibledisplay, according to an embodiment of the present invention.

The substrate 1000 according to the current embodiment of the presentinvention includes a plastic substrate 50, and a barrier layer 100disposed on the plastic substrate 50.

The plastic substrate 50 has flexibility enough to realize a flexibledisplay. Also, the plastic substrate 50 may have a thin film structurefor the flexibility.

The plastic substrate 50 may have a glass transition temperature (Tg)from about 350° C. to about 500° C. With this feature, the plasticsubstrate 50 can stably perform functions of a substrate without beingdeformed even when the barrier layer 100, a thin film transistor, and anelectronic device are formed on the plastic substrate 50 at hightemperature. In detail, the barrier layer 100 is formed at a temperaturefrom about 350° C. to about 400° C. Accordingly, if the Tg of theplastic substrate 50 is less than about 350° C. the plastic substrate 50may change to a rubber having elasticity at about 350° C. and thus maybe unable to perform the functions of substrate. On the other hand, theplastic substrate 50 having the Tg exceeding about 500° C. has badprocessability.

The plastic substrate 50 may be formed of a polymer having high thermalresistance. For example, the plastic substrate 50 may include at leastone material selected from the group consisting of polyethersulfone(PES), polyacrylate (PAR), polyetherimide (PEI), polyethylenenaphthalate (PEN), polyethylene terephthalate (PET), polyphenylenesulfide (PPS), polyarylate, polyimide (PI), polycarbonate (PC),cellulose triacetate (TAC), cellulose acetate propionate (CAP), andpoly(arylen ether sulfone) as a type of engineering plastic.Specifically, PI has excellent mechanical strength and has betterthermal resistance than other polymers as the Tg of PI is about 450° C.Accordingly, even when the bather layer 100 is disposed on the plasticsubstrate 50 including PI at high temperature, the plastic substrate 50may stably perform the functions of a substrate without drooping due toa weight of the barrier layer 100. Also, the plastic substrate 50including at least one of the above polymers has high level of oxygenand moisture penetration. Accordingly, when a thin film transistor andan electronic device are directly formed on the plastic substrate 50,the thin film transistor and the electronic device may be exposed tooxygen and moisture penetrating through the plastic substrate 50, andthus lifetime of a display may be remarkably reduced. The barrier layer100 is provided for blocking the moisture and oxygen formed on theplastic substrate 50.

In embodiments, the barrier layer 100 is formed on the plastic substrate50, and may hate a multi-layer structure, wherein at least one siliconoxide (SiO_(x)) layer and at least one silicon nitride (SiN_(x)) layerare alternately stacked on each other. The barrier layer 100 forms aflat surface on the plastic substrate 50 and blocks unwanted substances,such as oxygen and moisture, from penetrating through the plasticsubstrate 50. The barrier layer 100 may be formed using a plasmaenhanced chemical vapor deposition (PECVD) method using plasma. However,forming the barrier layer 100 is not limited thereto, and any depositionmethod may be used, such as an atmospheric pressure CVD (APCVD) methodor a low pressure CVD (LPCVD) method. According to an embodiment of thepresent invention, the barrier layer 100 is formed at high temperatureso that the barrier layer 100 is thin, has a uniform stress, and has ahigh film density. Specifically, in embodiments, since the plasticsubstrate 50 having a high Tg, is used, the barrier layer 100 may beformed at high temperature.

In embodiments, the barrier layer 100 is formed at a temperature fromabout 350° C. to about 400° C. Accordingly, the barrier layer 100 may beformed to have a uniform film stress, a thin thickness, and a high filmdensity to effectively block moisture and oxygen. Characteristics of thebarrier layer 100 will now be described in detail.

Referring to FIG. 1, the barrier layer 100 according to the currentembodiment of the present invention includes a first silicon oxide layer101 formed on the plastic substrate 50, a first silicon nitride layer201 formed on the first silicon oxide layer 101, and a second siliconoxide layer 102 formed on the first silicon nitride layer 201. Here, thefirst and second silicon oxide layers 101 and 102 may each have a filmstress from about −100 MPa to about −300 MPa, and the first siliconnitride layer 201 may have a film stress from about −50 MPa to about 200MPa. The film stress denotes a size of strength of a thin film layer perunit area, and may be compressive film stress or tensile film stress.Here, the compressive film stress is indicated with a negative integer,and the tensile film stress is indicated with a positive integer. Also,the compressive film stress may be power pushing a thin film to bend thethin film downward. On the other hand, the tensile film stress may bepower pulling a thin film to bend the thin film upward.

In embodiments, each of the first and second silicon oxide layers 101and 102 may have compressive film stress, and the first silicon nitridelayer 201 may have tensile film stress. Accordingly, with the structure,in which the first silicon oxide layer 101, the first silicon nitridelayer 201, and the second silicon oxide layer 102 are alternativelystacked and have different types of film stresses, the barrier layer 100becomes strong against external shock or bending. Also, the substrate1000 does not affect a thin film transistor and an electronic devicedisposed on the barrier layer 100 in terms of stress.

The barrier layer 100 has a film stress from about −200 MPa to about 200MPa. When the film stress of the barrier layer 100 is below about −200MPa or above about 200 MPa, the substrate 1000 including the barrierlayer 100 may bend upward or downward. In this case, the substrate 1000may be stuck in an equipment during transference or operation. Also,when the film stress of the barrier layer 100 is below about −200 MPa orabove about 200 MPa, dislocation may be generated at an interfacebetween a top surface of the barrier layer 100 and another thin filmdisposed on the top surface of the barrier layer 100 due to an excessivestress. Such dislocation deteriorates characteristics of the thin filmtransistor and the electronic device disposed on the barrier layer 100.Besides, film quality of the other film disposed on the barrier layer100 may deteriorate, thereby deteriorating electric characteristics ofthe electronic device or causing a defect in the electronic device.Alternatively, the barrier layer 100 may have a film stress of about 0MPa, because the film stress of the barrier layer 100 may becounterbalanced as the first and second silicon oxide layers 101 and102, and the first silicon nitride layer 201 have different filmstresses. Accordingly, even when the barrier layer 100 has the filmstress of 0 MPa, each of the first and second silicon oxide layers 101and 102 and the first silicon nitride layer 201 still has film stress.

Also, The thickness of the first silicon nitride layer 201 may be fromabout 200 Å to about 1000 Å. Here, the thickness of the first siliconnitride layer 201 is about 200 Å or above since 200 Å is a minimumthickness for forming a thin film. The thickness of the first siliconnitride layer 201 is limited to about 1000 Å or below due to thefollowing reason. When the first silicon nitride layer 201 is formed athigh temperature, hydrogen atoms are separated and escape from the firstsilicon nitride layer 201 as coherence between silicon atoms and thehydrogen atoms decreases, and thus a hydrogen atom content in the firstsilicon nitride layer 201 decreases. Accordingly, film stress of thefirst silicon nitride layer 201 changes from compressive film stress totensile film stress. At this time, when the thickness of the firstsilicon nitride layer 201 exceeds 1000 Å, the first silicon nitridelayer 201 may break or be detached.

In embodiments, each of the first and second silicon oxide layers 101and 102 may have a thickness from about 1000 Å to about 3000 Å. When thethickness of each of the first and second silicon oxide layers 101 and102 is below about 1000 Å, the first and second silicon oxide layers 101and 102 are difficult to be formed, and when the thickness of each ofthe first and second silicon oxide layers 101 and 102 is above about3000 Å, a time taken to form the first and second silicon oxide layers101 and 102 remarkably increases.

In embodiments. moisture and oxygen penetration may be controlled by thehydrogen atom content in the first silicon nitride layer 201 included inthe barrier layer 100.

In embodiments, the first silicon nitride layer 201 is formed at atemperature from about 350° C. to about 400° C. using the PECVDtechnique as follows. The plastic substrate 50 on which a layer isdeposited is put into a chamber, and a process temperature is set to befrom about 350° C. to about 400° C. under a plasma atmosphere. The firstsilicon nitride layer 201 is flamed with silane (SiH₄) and ammonia(NH₃). The silane is decomposed into silicon (Si) atoms and hydrogen (H)atoms, and the ammonia is decomposed into nitrogen (N) atoms andhydrogen atoms by plasma. These decomposed silicon, hydrogen, andnitrogen atoms fall onto the plastic substrate 50, and react to formsilicon nitride at surface temperature of the plastic substrate 50.Here, the nitrogen atoms and the hydrogen atoms combine with the siliconatoms. Since coherence between the silicon atoms and the hydrogen atomsis weaker than coherence between the silicon atoms and the nitrogenatoms, even when the silicon atoms and the nitrogen atoms maintain thecoherence, the silicon atoms and the hydrogen atoms are separated fromeach other at high temperature. As a result, the hydrogen atomsseparated from the silicon atoms form hydrogen molecules (H₂) anddisappear. Accordingly, when the first silicon nitride layer 201 isformed at high temperature, the hydrogen atom content in the firstsilicon nitride layer 201 is low. Also, as the hydrogen atom content inthe first silicon nitride layer 201 decreases, i.e., as the coherencebetween the nitrogen atoms and silicon atoms increases, the film stressof the first silicon nitride layer 201 becomes more tensile. Also, asthe hydrogen atom content in the first silicon nitride layer 201decreases, film density of the first silicon nitride layer 201increases.

In embodiments, the hydrogen atom content in the first silicon nitridelayer 201 may be from about 13% to about 17%, because the hydrogen atomcontent in the first silicon nitride layer 201 depends on thetemperature of forming silicon nitride. Experimentally, when a siliconnitride layer is deposited at a temperature from about 350° C. to about400° C., hydrogen atom content in the silicon nitride layer is fromabout 13% to about 17%. Also, if the hydrogen atom content in the firstsilicon nitride layer 201 is below about 13%, film density of the firstsilicon nitride layer 201 may increase, but tensile film stress of thefirst silicon nitride layer 201 increases above a threshold value andthus a stress balance of the barrier layer 100 may break. On the otherhand, if the hydrogen atom content in the first silicon nitride layer201 is above about 17%, the film density of the first silicon nitridelayer 201 may remarkably decrease, and thus unwanted substances, such asoxygen and moisture, may penetrate into the thin film transistor and theelectronic device.

In embodiments, the film density of the first silicon nitride layer 201may be from about 2.5 g/cm³ to about 2.7 g/cm³. The film density of thefirst silicon nitride layer 201 depends on the hydrogen atom content inthe first silicon nitride layer 201. When the hydrogen atom content inthe first silicon nitride layer 201 is from about 13% to about 17%, thefilm density of the first silicon nitride layer 201 may be from about2.5 g/cm³ to about 2.7 g/cm³. If the film density of the first siliconnitride layer 201 is below about 2.5 g/cm³, the function of the firstsilicon nitride layer 201 for blocking impure elements, such as oxygenand moisture, from penetrating into the thin film transistor and theelectronic device may remarkably deteriorate. On the other hand, thefilm density of the first silicon nitride layer 201 is difficult toexceed about 2.7 g/cm³ if the hydrogen atom content is from about 13% toabout 17%.

FIG. 2 is a cross-sectional view of a substrate 1000 a for a flexibledisplay, according to another embodiment of the present invention.Referring to FIG. 2, the substrate 1000 a is similar to the substrate1000 as at least one silicon oxide layer and at least one siliconnitride layer are alternately stacked on the plastic substrate 50.However, barrier layer 100 a of the substrate 1000 includes the firstsilicon oxide layer 101, the first silicon nitride layer 201 disposed onthe first silicon oxide layer 101, the second silicon oxide layer 102disposed on the first silicon nitride layer 201, a second siliconnitride layer 202 disposed on the second silicon oxide layer 102, and athird silicon oxide layer 103 disposed on the second silicon nitridelayer 202. Here, discussions of the barrier layer 100 of FIG. 1 are allapplicable to the barrier layer 100 a. Specifically, the characteristicsof the barrier layer 100 of FIG. 1 are all applicable to thecharacteristics of the barrier layer 100 a, including thicknesses, typesof film stresses, contents of hydrogen atoms, film densities. Also, themethod of making the oxide layers 101, 102 and nitride layer 202 of theembodiment of FIG. 1 and conditions of forming these layers are alsoapplicable to the embodiment of FIG. 2. Thus, the discussions are notrepeated.

FIG. 3 is a cross-sectional view of a substrate 1000 b for a flexibledisplay, according to another embodiment of the present invention.Referring to FIG. 3, the substrate 1000 b is similar to the substrates1000 and 1000 a as at least one silicon oxide layer and at least onesilicon nitride layer are alternately stacked on the plastic substrate50. However, barrier layer 100 b of the substrate 1000 b includes thefirst silicon oxide layer 101, the first silicon nitride layer 201disposed on the first silicon oxide layer 101, the second silicon oxidelayer 102 disposed on the first silicon nitride layer 201, the secondsilicon nitride layer 202 disposed on the second silicon oxide layer102, the third silicon oxide layer 103 disposed on the second siliconnitride layer 202, a third silicon nitride layer 203 disposed on thethird silicon oxide layer 103, and a fourth silicon oxide layer 104disposed on the third silicon nitride layer 203. Here, discussions ofthe barrier layer 100 of FIG. 1 are all applicable t the barrier layer100. Specifically, the characteristics of the barrier layer 100 of FIG.1 are all applicable to the characteristics of the barrier layer 100 b,including thicknesses, types of film stresses, contents of hydrogenatoms, film densities. Also, the method of making the oxide layers 101,102 and nitride layer 202 of the embodiment of FIG. 1 and conditions offorming these layers are also applicable to the embodiment of FIG. 3.Thus, the discussions are not repeated.

FIGS. 4 through 6 are diagrams for describing a method of manufacturinga display device by using the substrate 1000 of FIG. 1, according to anembodiment of the present invention. Specifically, FIGS. 4 and 5 arediagrams for describing a method of manufacturing the substrate 1000.For the convenience of description, only the method used for thesubstrate 1000 is described. However, the same method will also beapplied to the substrates 1000 a and 1000 b.

Referring to FIG. 4, first, the plastic substrate 50 is prepared. The Tgof the plastic substrate 50 may be from about 350° C. to about 500° C.so that the plastic substrate 50 stand high temperature treatments.

Referring to FIG. 5, the barrier layer 100 is formed on the plasticsubstrate 50. Here, the barrier layer 100 is formed at a temperaturefrom about 350° C. to about 400° C. according to a PECVD method. Indetail, the barrier layer 100 includes the first silicon oxide layer 101formed on the plastic substrate 50, the First silicon nitride layer 201formed on the first silicon oxide layer 101, and the second siliconoxide layer 102 formed on the first silicon nitride layer 201. Here, thethickness of each of the first and second silicon oxide layers 101 and102 is from about 1000 Å to about 3000 Å, and the thickness of the firstsilicon nitride layer 201 is from about 200 Å to about 1000 Å. Each ofthe first and second silicon oxide layers 101 and 102 has compressivefilm stress, and the first silicon nitride layer 201 has tensile filmstress. Also, the film stress of the barrier layer 100 is from about−200 MPa to about 200 MPa. Here, if the film stress of the barrier layer100 is outside the above range, the substrate 1000 could bend, ordislocation could occur in the interface between the barrier layer 100and a device that is formed on the barrier layer 100 due to the filmstress.

In embodiments, the first silicon nitride layer 201 included in thebarrier layer 100 may be formed at a temperature from about 350° C. toabout 400° C. according to a PECVD method, by using silane and ammonia.In embodiments, the first silicon nitride layer 201 formed as describedabove has a hydrogen atom content from about 13% to about 17%, and afilm density from about 2.5 g/cm³ to about 2.7 g/cm³. In embodiments,when the hydrogen atom content in the first silicon nitride layer 201 isfrom about 13% to about 17%, the film density of the first siliconnitride layer 201 may be from about 2.5 g/cm³ to about 2.7 g/cm³ and thefirst silicon nitride layer 201 may block moisture and oxygen suitablyto manufacture the display device.

Referring to FIG. 6, in embodiments, a semiconductor active layer 10,including a source region 10 s, a drain region 10 d, and a channelregion 10 c, is patterned and formed on the barrier layer 100, and afirst insulation layer 11 is formed on the semiconductor active layer10. A gate electrode 20 g corresponding to the semiconductor activelayer 10 is formed on the first insulation layer 11, and a secondinsulation layer 12 is formed on the gate electrode 20 g. A contact hole(not shown) is formed in the first and second insulation layers II and12, and a source electrode 20 s and a drain electrode 20 d are formed onthe second insulation layer 12 and are electrically connected to thesemiconductor active layer 10 through the contact hole, therebycompleting the manufacture of a thin film transistor. Also, although notillustrated in FIG. 6, a flexible display may be manufactured by furtherforming a capacitor and an electronic device such as an organic lightemitting device (OLED).

When the barrier layer is not formed at high temperature, the siliconoxide layer and silicon nitride layer may need to be thick so as toprevent moisture and oxygen from penetrating, Alternatively, when thebarrier layer is formed at a low temperature, particles of the barrierlayer are loose, and thus film stress of the barrier layer is high and ahydrogen atom content is high. Accordingly, film density of the barrierlayer is low. As a result, when the barrier layer is formed at lowtemperature, the barrier layer may have a high film stress, and thus athin film transistor and an electronic device are adversely affected,moisture and oxygen blocking characteristics are, low. However,according to embodiments of the present invention, these can be resolvedby forming the barrier layer at high temperature and with the use of aplastic substrate having a high Tg.

FIG. 6 illustrates a top gate thin film transistor that can be formedover a barrier layer according to embodiments of the invention. However,alternatively a bottom gate thin film transistor can be formedsimilarly. Also, only one thin film transistor is shown in FIG. 6, butthis is only for convenience of description, and a plurality of thinfilm transistors, a plurality of capacitors, or a plurality of OLEDs maybe included.

In addition, in FIG. 6, the substrate 1000 is used as a lower substrateformed below the thin film transistor and the electronic device, but thesubstrate 1000 may also be disposed in an encapsulating member, in otherwords, the encapsulating member including the substrate 1000 isseparately formed, and the encapsulating member is combined to an OLED,thereby easily encapsulating the OLED.

Also, the substrate 1000 may be used for any one of various flat displaydevices, such as organic light emitting display devices and liquidcrystal display devices.

According to a substrate for a flexible display and a method ofmanufacturing the substrate according to one or more embodiments of thepresent invention, a barrier layer is formed on a plastic substrate athigh temperature, and thus the substrate having a thin thickness andfilm stress range that does not adversely affect a thin film transistorand an electronic device may be provided.

Also, the barrier layer includes a silicon nitride layer that has a lowhydrogen atom content in the silicon nitride layer. Thus, the siliconnitride layer has a high film density, thereby highly efficientlyblocking moisture and oxygen penetration.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A flexible display, comprising: a flexible substrate; a barrier layeron the flexible substrate, wherein the barrier layer comprises a firstsilicon oxide layer, a second silicon oxide layer disposed under thefirst silicon oxide layer, and a first silicon nitride layer interposedbetween the first silicon oxide layer and the second silicon oxide layerso as to directly contact the first silicon oxide layer and the secondsilicon oxide layer, respectively; a thin-film transistor on the barrierlayer, wherein thin-film transistor comprises a semiconductor activelayer and a gate electrode disposed on the semiconductor layer and thatat least partially overlap with each other; and a first insulation layerinterposed between the semiconductor active layer and the gateelectrode, wherein the semiconductor active layer and first insulationlayer are dispose(directly on the barrier layer, and wherein the firstsilicon oxide layer and the second silicon oxide layer have acompressive or tensile type of film stress, and the first siliconnitride layer has a different type of film stress than the first siliconoxide layer and the second silicon oxide layer, and the barrier film hasa film stress of −200 MPa to 200 MPa.
 2. The flexible display of claim1, wherein the first silicon nitride layer and the second siliconnitride layer have a hydrogen atom content from about 13% to about 17%.3. The flexible display of claim 1, wherein each of the first siliconoxide layer and the second silicon oxide layer has a compressive filmstress, and the first silicon nitride layer has a tensile film stress.4. The flexible display of claim 1, wherein each of the first siliconoxide layer and the second silicon oxide layer has a compressive filmstress from about 300 MPa to about 100 MPa, and wherein the firstsilicon nitride layer has a tensile film stress from about −50 MPa toabout 200 MPa.
 5. The flexible display of claim 1, wherein a filmdensity of the first silicon nitride layer is from about 2.5 g/cm3 toabout 2.7 g/cm3.
 6. The flexible display of claim 1, wherein a thicknessof the first silicon nitride layer is thinner than a thickness of one ofthe first silicon oxide layer and the second silicon oxide layer.
 7. Theflexible display of claim 6, wherein the thickness of the first siliconnitride layer is from about 200 Å to about 1000 Å and the thickness ofeach of the first silicon oxide layer and the second silicon oxide layeris from about 1000 Å to about 3000 Å.
 8. The flexible display of claim1, wherein the barrier layer comprises: a second silicon nitride layerstacked under the second silicon oxide layer; and a third silicon oxidelayer stacked under the second silicon nitride layer.
 9. The flexibledisplay of claim 8, wherein the barrier layer comprises: a third siliconnitride layer stacked under the third silicon oxide layer, and a fourthsilicon oxide layer stacked wider the third silicon nitride layer. 10.The flexible display of claim 1, wherein the plastic substrate comprisespolyimide.
 11. The flexible display of claim 1, further comprising: anorganic light-emitting device (OLED) in electric contact with thethin-film transistor, and an encapsulating member that encapsulates theOLED.
 12. The flexible display of claim 1, wherein the flexiblesubstrate comprises a plastic substrate that has a glass transitiontemperature from about 350° C. to about 500° C.